Observation of the four-photon de Broglie wavelength by state-projection measurement

摘要

A measurement process is constructed to project an arbitrary two-mode N-photon state to a maximally entangled N-photon state. The result of this projection measurement shows a typical interference fringe with an N-photon de Broglie wavelength. For an experimental demonstration, this measurement process is applied to a four-photon superposition state from two perpendicularly oriented type-I parametric down-conversion processes. Generalization to the projection measurement of an arbitrary N-photon state can be easily made and may have wide applications in quantum information. As an example, we formulate it for precision phase measurement.